This invention relates to semiconductor diodes, and, more particularly, to a modified double barrier tunnel diode.
A diode is a semiconductor device having a nonlinear voltage-current relation. Diodes are among the most important of solid-state devices, and are used in many electronic applications. The tunnel diode is one variety of diode, having the unusual characteristic of negative resistance. As the term is used, negative resistance is a voltage-current behavior wherein, over certain voltage ranges, increasing the voltage applied across the diode leads to decreased current carried through the diode. By contrast, in most devices an increasing applied voltage results in increasing current. Tunnel diodes have a number of applications, including high frequency oscillator circuits and high frequency electronic switches.
One type of tunnel diode is the double barrier tunnel diode. One such double barrier tunnel diode includes a gallium antimonide quantum well with a thin barrier layer of aluminum antimonide epitaxially joined to each side of the quantum well. This structure, termed a quantum barrier, in turn lies between two injection layers of indium arsenide. The quantum barrier creates an energy barrier to the flow of electrons that can be overcome by electrons only under certain conditions, and which results in the negative resistance characteristic of interest over a range of applied bias voltage. Electrons are injected into the quantum barrier from the conduction band of one of the injection layers under an internal voltage, produced by the applied external voltage. The internal voltage increases the energy of the injected electrons to satisfy the resonant tunneling condition of the quantum barrier. Under the proper conditions of voltage sufficient to satisfy the resonance condition, the incoming electron has the same energy as a valence level of the quantum well, and the electrons tunnel through the quantum barrier. As the bias voltage is increased further, the energy levels no longer align and the current decreases, resulting in the negative resistance effect.
In some cases, it has been observed that the magnitude of the negative resistance effect is not as great as might be expected. It is important to understand the cause of this reduced negative-resistance effect, and an associated need for an improved double barrier tunnel diode that exhibits the full extent of the negative-resistance effect. The present invention fulfills this need, and further provides related advantages.